Down-hole tools such as mud motors that are hydrostatically driven and therefore rotatable relative to the drill string are used to drive the drill bit. Rather than having a larger surface motor rotate the entire drill string, a down-hole mud motor rotates the drill bit. This arrangement is especially useful in horizontal bores.
Generally, such motors utilize some type of bearing so that the down-hole mud motor is allowed to rotate relative to the drill string. These down-hole motors are subjected to a very hostile environment such as exposure to high heat, vibration, and high velocity solids. Accordingly, it is not uncommon for the motor bearings to fail. Bearing failure causes the motor to stall. However, since the operators of the drilling operation are ordinarily unaware of such failure and thus continue driving the down-hole motor, the continued rotational force applied to the drill bit by the down-hole mud motor power section has a tendency to rotate the portion of the motor housing located below the power section. Rotation of these sections of the down-hole motor housing eventually results in at least one of the sections and the drill bit becoming separated from the remainder of the down-hole mud motor housing and possibly being lost in the well bore. If the motor housing and bit are lost in the well bore, generally it is time consuming and expensive to perform fishing operations in an attempt to retrieve the lost components. When these relatively expensive components cannot be retrieved, they generally continue to impede further drilling operations.
Various methods have been employed within the art to overcome the above stated problem. For example Falgout and Beasley, in U.S. Pat. Nos. 6,540,020 and 5,165,492 respectively, disclose a valve having means for biasing the valve against rotation of the housing in a manner that allows the flow of fluid to the motor to be cut off if the fluid motor housings and bit separate. It is suggested that this restriction in fluid flow will alert the operators on the surface that a problem exists and thus initiate a removal of the mud motor procedure for inspection. A sudden disruption of flow in the form of a blockage at high pressure in excess of 6000 psi certainly tends to get someone's attention when the surface pump is destroyed as a result. In addition, once the fluid to the down-hole motor is shut off, it becomes very difficult to withdraw the drill string. In such cases, extraordinary measures must be taken to free the bit manually and retrieve the drill string.
The present invention is directed to overcoming or minimizing one or more of the problems discussed above.